Had it occasionally on my drivers door, then a week or so ago wouldn't open (from the outside) at all, had to climb in through the boot!!!
The outside handle didn't appear to have the same resistance as usual/passenger side. On removing the latch mechanism all seemed ok with the mechanical items, cables etc were fine.
As I'd already got a replacement latch (ordered just in case) & the door card was off I replaced the latch (easy job) & all is fine, door lock & handle feel much better now so can only assume something has broken inside the latch assembly itself.